The largest share of student loan deadbeats are celebrating their 25th college reunions.

Borrowers age 40-49 have the highest proportion of loans that are at least 90 days behind, according to new data published by the Federal Reserve Bank of New York. And that's been true each quarter since 2005.

Here's a profile of who holds student loans as of the first quarter of 2012:

There are 14 million more student loan borrowers now than there were in 2005, for a total of 37 million.

About 25 million are age 39 and under.

More than 7 million are age 50 and older.

And then it comes to debt levels:

Thirty-somethings have the largest share of debt, about 1/3, or $307 billion. On average, their balance is $28,906.

Debt levels of those in their 50s increased to $106 billion, from $34 billion in 2005. The average balance is $23,183.

Those age 60-plus are now carrying more than $43 billion, up from $8 billion. Their average balance is $19,225.

The explosion in student loans -- as well as mounting delinquencies -- has some experts worrying that it's the next financial bubble to pop.